The formation of titanium carbide from various titanium oxide-containing materials as an intermediate for the formation of pigmentary TiO.sub.2 is known. The reaction which produces the titanium carbide in the prior art is carburization of the titanium oxide-containing material, usually in the form of a slag from ore processing.
Titanium occurs with iron in natural deposits of ilmenite ore. The titanium and iron values are present in the form of their oxides (FeO. TiO.sub.2), along with gangue constituents, mainly alumina, silica, magnesia and lime. One prior art procedure for the recovery of the titanium and iron values from the ore is described in U.S. Pat. No. 3,899,569 and in "Titanium Carbide from Domestic Titanium Ores" by W. L. Hunter et al, TMS/AIME Preprint A73-18, Ch. 73, pp 257 to 270.
In this known procedure, electric furnace smelting of ilmenite with coke and lime is effected under conditions which favour reduction of iron oxide to iron, to result in a pig iron product and a slag in which the titanium values are mainly in the form of calcium titanate. The slag is subjected to a solid state carburization reaction at high temperatures of from about 1850.degree. to about 3150.degree. C. to form a mixture of calcium, titanium, iron and aluminum carbides. Silica present in the slag is reduced to SiO and is volatilized. The mixed carbides are cooled, crushed and reacted with water, thereby forming acetylene and calcium hydroxide from the calcium carbide and liberating the titanium carbide.
The titanium carbide then may be chlorinated at relatively low temperatures usually in the range of about 200.degree. to about 500.degree. C. to selectively convert the titanium carbide to pure gaseous titanium tetrachloride, while leaving any impurities in the solid phase. The titanium tetrachloride then may be oxidized to high purity pigmentary TiO.sub.2.
While this prior art process is attractive, in that the titanium values are provided in the form of pure TiCl.sub.4, from which pure TiO.sub.2 pigment may be readily produced, and iron is also recovered in a useful form, the procedure suffers from the drawback that a considerable energy requirement is needed to effect first the smelting and then the high temperature carburization of the slag and that a multiple number of processing steps is required to be effected on the ore before titanium carbide suitable for chlorination results.